I had the same issue with mine.
The car was only a year and a half old and I noticed the air con was just blowing warm air out (I set it to low I promise)
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Anyway, when they tested the system, they found pinhole leak in one of the pipes!
Once again, Renault tried to say I caused it but with the list of problems I was having with the car, it didn't take them too long to back down and do it!
Replaced the pipe and a full recharge under warranty!
Worried the same will happen in the next two years though. The dealer told me that they use the same system as the Qashqai and they are having terrible trouble with their air con systems! GREAT!